1. Field of the Invention
The present invention relates generally to portable bulk transfer pumps. More particularly, the present invention concerns a portable bulk transfer pump having a variable speed drive for the pump to enable the pumping of fluids having varying viscosities.
2. Discussion of Prior Art
Portable bulk transfer pumps are known in the art. These prior art pumps typically include a fixed speed electric motor powering a positive displacement pump, all of which is carried on a portable hand cart. These pumps are used to transfer various types of liquids. For example, in the oil industry, retailers utilize these prior art pumps to transfer lubricants from their initial bulk storage tanks to more convenient containers utilized in the retailer's plant. Such transfers may take place at many different locations in a single plant. Accordingly, these prior art pumps are readily and easily moved by hand. These prior art pumps are typically powered by 115 VAC outlets connected to 20 amp (or less) circuit breakers, which is the typical power system utilized in most plants. Suitable examples of these prior art portable bulk transfer pumps are Applicant's High Volume Transfer Pump and Light Viscosity Bulk Transfer Cart, available from Applicant as Part Nos. 33267 and 33271, respectively.
Although Applicant's prior art pumps are well advanced in the art, they, along with all prior art portable bulk transfer pumps, are subject to several problems and undesirable limitations. For example, a single retailer may have a plurality of different fluids that need transferred ranging from thin viscosity fluids, such as hydraulic fluids, light-weight engine oils (5W or 10W), and antifreeze, to medium viscosity fluids, such as 10W-30 or 10W-40 engine oils, to high viscosity gear oils, such as 80, 90, or 140 weight gear oils. Additionally, the viscosity of a particular fluid may change quite drastically with changes in temperature. It is common practice to have bulk lubricant products stored in unheated warehouses and delivered in unheated trucks. Therefore, if a prior art pump is configured to operate at a relatively high rate to pump a low viscosity fluid, it is inefficient and ineffective at pumping a high viscosity fluid. Furthermore, the power systems utilized in most plants severely limit the ability to transfer oil having relatively thick viscosities at high rates without causing the circuit breaker to open. To combat these problems, lubricant retailers have previously resorted to purchasing many types of pumps, each capable of handling fluids within narrow viscosity ranges (i.e., one pump for thin fluids, one pump for medium viscosity fluids, and one pump for highly viscous fluids). Such a practice is inefficient from a capital expense standpoint and can often times leave delivery personnel in the situation of not having the right pump for the right task. Heretofore, no single portable bulk transfer pump has been able to accommodate fluids having wide ranging viscosity values. Accordingly, there is a real and unfulfilled need in the art for an improved portable bulk transfer pump that is capable of handling fluids having widely varying viscosities in a timely and efficient manner.